WSP07593 - Laserfiche WebLink

Home Browse Search

Aspen HjghlcuuJs Ski Area - Draft Enviro/IIUnlaJ Impact Slale~nl POTENTIAL MITIGATION MEASURES The top terminals of the Steeplechase, Highland Bowl, and Maroon Bowl lifts should be located to avoid gravitational cracks. Lift and building fOlmdations will be designed to withstanding stresses and strains due to gravitational spreading, and lift tower fOlmdations will be anchored in stable rock beneath actively moving talus. SlDVey monuments should be placed in the Loge Peak area to monitor movements due to gravitational spreading. To reduce the risk of slope failure, the venical disturbance of slope cuts along catwalks/access roads should not exceed 8 feet and retaining walls should be used to minimi7e fillslope failure and downslope disturbance widths. Rockfall prevention measures will be implemented, and signs warning visitors of rockfall hazards will be erected. A drainage system capable of effectively diverting spring run-off away from steep, inherently unstable slopes will be designed and constructed using Forest Service best management practices (BMPs). Debris flow hazards, especially along the Lower Temerity maintenance road, could be reduced by dipping the road across the active channel and by constructing debris flow crossings sufficiently large to accommodate potential flow contents. WATERSHED RESOURCES AFFECTED ENVIRONMENT The Aspen Highlands ridgeline divides the Maroon Creek watershed (MCW) and the Castle Creek watershed (CCW), and the surface flow of both discharges into the Roaring Fork River. The MCW ranges in elevation from 7,760 to 12.200 feet and encompasses 1,943 acres, and the CCW ranges in elevation from 8,100 to 12,400 feet and encompasses 2,20 I acres. There are a series of drainages on either side of the ridge, most of which are less than 100 acres in size. Two hydrographic areas within each watershed, each with a single outlet for surface flow, were analyzed in detail because they incorporate runoff from a relatively significant portion of the current and potential future developments. MCW-A, the more southerly of the two hydrographic areas in the MCW, contains three first-order channels that converge near 9,400 feet elevation. The middle channel is perennial and spring fed, while the other two channels are intennitteot. The drainage channel in the MCW-B hydrographic area is intermillent. The main channel draining CCW-A, the southern hydrographic area in CCW, is spring fed and perennial with several intennillent channels connecting to it. The northern hydrographic area in CCW, CCW-B is spring fed and flows intermittently near 10,000 feet elevation. During developmeot of Aspen Highlands, substantial grading reshaped topographic features, including stream channels. The removal of forest cover and substantial disturbance of soil 10 construct ski runs, lift lines, catwalks, and maintenance roads has increased overland flow and the risk of erosion. Efforts to control runoff and sedimentation have led to a system of drainage ditches that carry water long distances before discharging it onto steep hillslopes draining into Maroon Creek. This system resulted in a debris flow into Maroon Creek in 1995 following an accumulation of abnormally deep snowpack and subsequent rapid snowmelt. In addition, during a heavy rainstorm in 1990, muddy water from the ski area flowed into Maroon Creek temporarily reducing water quality. Many of the ski runs located in the MCW have been graded and occupy 17 percent of the composite watershed, and roads and catwalks occupy a density of 2.8 miles per square mile (l percent of MCW). No evidence of overland flow or erosion were found where vegetative cover was left undisturbed or was effectively restored following ski run construction. However, despite efforts to divert runoff to undeveloped portions of the ski area, rills and gullies have formed where brush was removed along runs with sparse ground cover, on graded runs and slopes that were ineffectively revegetated or that are traversed by a road, and along the tire tracks where soil has been compacted. Diversion ditches have also contributed to erosion of both the developed and undeveloped areas, and outflows from the ditches have sometimes been sufficient to destabilize slope ooto which water is discharged. In the CCW, ski area development is less than I percent of the total area, and road density is 0.8 miles per square mile (less than 1 percent of the watershed). Most of the development lies in the upper elevations of this 16 Sectjon III Walers~d Resources